Splice joint in laminate composite structure

ABSTRACT

Layers of plies of composite material are laid on a convex tool surface. A first layer is placed with a first ply of a first section having a gap edge adjacent a gap edge of a first ply of a second section, the edges being parallel and a contraction distance from each other. A second layer is placed with a second ply of the first section having a gap edge adjacent a gap edge of a second ply of the second section, the edges being parallel and a contraction distance from each other, the second ply of the second section overlapping onto the first ply of the first section by a splice distance. Consolidation and curing cause contraction of the layers toward the tool, allowing the adjacent gap edges of each layer to be in close proximity or in contact after moving toward each other during the contraction.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND

Composite laminate structures are formed from a plurality of plies offibers and a matrix material. The fibers of the plies may be generallyparallel, as in unidirectional tape, or at angles to each other, as inwoven mats or chopped fiber applications. The matrix material of theplies may be impregnated before placement, known as “prepreg,” appliedmanually, such as by brushing, or injected into a mold containing placedfibers.

Prepreg plies are produced with a selected volume of matrix material,and uncured-ply thickness is larger than the cured-ply thickness due tothe change in volume or redistribution of matrix material duringconsolidation and curing. Excess matrix material may escape from theplies during consolidation, such as during vacuum bagging of thestructure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of an aircraft having a structure formed using amethod according to this disclosure.

FIG. 2 is a cross-section oblique side view of an uncured splice jointformed using a prior art method.

FIG. 3 is a cross-section side view of another uncured structure havinga splice joint formed using a prior art method.

FIG. 4 is an exploded cross-section side view of a splice jointaccording to this disclosure.

FIG. 5 is an enlarged oblique cross-section side view of a portion ofthe splice joint of FIG. 4.

FIG. 6 is an exploded cross-section side view of another embodiment of asplice joint according to this disclosure.

FIG. 7 is a cross-section side view of an uncured splice joint accordingto this disclosure.

FIG. 8 is a cross-section side view of the splice joint of FIG. 7 aftercuring.

FIG. 9 is an oblique view of a section of a cured structure with asplice joint according to this disclosure.

FIG. 10 is an exploded oblique cross-section side view of anotherembodiment of a splice joint according to this disclosure.

DETAILED DESCRIPTION

In this disclosure, reference may be made to the spatial relationshipsbetween various components and to the spatial orientation of variousaspects of components as the devices are depicted in the attacheddrawings. However, as will be recognized by those skilled in the artafter a complete reading of this disclosure, the devices, members,apparatuses, etc. described herein may be positioned in any desiredorientation. Thus, the use of terms such as “above,” “below,” “upper,”“lower,” or other like terms to describe a spatial relationship betweenvarious components or to describe the spatial orientation of aspects ofsuch components should be understood to describe a relative relationshipbetween the components or a spatial orientation of aspects of suchcomponents, respectively, as the device described herein may be orientedin any desired direction.

The splice joints and methods of forming splice joints disclosed hereinare used to join plies of sections of an uncured composite structureprior to curing. The embodiments of this method are useful forminimizing wrinkles or voids in a cured laminate composite, which may beformed from unidirectional tape laid by an automated fiber-placement(AFP) machine, on a tool with a convex surface. The joint and method areespecially useful with tools having a closed-shape cross section, suchas, for example, a mandrel on which plies are laid for forming a hollowstructure. The figures are simplified, schematic views, used forillustration only, and are not to scale.

FIG. 1 illustrates a helicopter 101, comprising a fuselage 103 and atailboom 105 extending rearward from fuselage 103. Fuselage 103 andtailboom 105 are typically formed as laminate composite structures, inwhich AFP machines lay prepreg unidirectional tape on a closed-shapetool in selected ply directions to achieve the strength required for theapplication. In helicopter 101, fuselage 103 and tailboom 105 are formedas separate structures and typically joined together with fastenersafter curing. Because of the complex shape with small radii, splicejoints are preferably used in at least transition region 107 and may beused on any closed shape, such as the remainder of fuselage 103 ortailboom 105.

Prepreg ply thickness varies before and after curing due to the matrixmaterial content and location. During part consolidation and curing, thematrix material may escape from around the fibers of each ply and flowbetween and around the fibers of other plies to consolidate the part.During this reaction, the plies will shrink, and the fibers will moverelative to adjacent fibers and/or adjacent layers of plies. The pliesmove inward toward the tool as the thickness of each underlying plydecreases. This can be especially problematic when manufacturing aclosed-shape part (e.g., cylinder, rectangular box, etc.) on a male toolwhen there is no “free edge” for the material to allow fiberdisplacement during part consolidation and cure. On thick laminates (6plies or more) with a small tool radius, this can cause wrinkles, whichare undesirable due to stress concentrations at the fiberdiscontinuities. Laminates with more plies would make it even lesslikely that fibers would be able to move during consolidation andcuring.

FIGS. 2 and 3 illustrate prior-art uncured splice joints, with FIG. 2being an oblique cross-section side view and FIG. 3 being across-section side view. Prior-art splice construction is usually stagedand repeated every five plies (per manufacturer guidelines), which tendsto trap all fibers and limits fiber displacement during cure due to theoverlapping sequence.

FIG. 2 shows a portion of an uncured structure 109, comprising twolayers A, B of plies of composite prepreg laid on a tool 111. As shown,each layer typically comprises multiple parallel tapes 112 ofunidirectional fibers laid adjacent one another. A tool surface 113 isshown as generally flat, though tool surface 113 may be a small portionof a larger tool having a convex shape. Base layer A comprises two plies115, 117, and layer B comprises plies 119, 121. Plies 115, 117, 119, 121may be, for example, unidirectional tape with longitudinal fibersextending generally perpendicularly to the view plane (0 degrees),parallel to the view plane (90 degrees), or oblique to the view plane(e.g., +/−45 degrees).

As shown, plies 115, 119 extend longitudinally from a first section, andplies 117, 121 extend longitudinally from a second section, the firstand second sections being joined by the splice joint to form structure109. Plies 115, 117, 119, 121 extend longitudinally and terminate atlateral edges, only one edge for each ply being shown. Ply 115 has edge123, ply 117 has edge 125, ply 119 has edge 127, and ply 121 has edge129. In the following discussion, the arrangement of plies 115, 117,119, 121 are described, but it should be noted that the placement stepsmay be completed in a different but appropriate order than is presented.

To form the prior-art splice joint, ply 115 is placed on tool surface113, and ply 119 is placed on ply 115. Edge 127 of ply 119 is spacedlongitudinally from edge 123 of ply 115, so that ply 115 longitudinallyextends beyond edge 127. Ply 117 is placed on tool surface 113, withlongitudinal portion 131 of ply 117 overlapping onto ply 115, with edge125 of ply 117 spaced from edge 123 of ply 115. This forms outward step133 where ply 117 meets edge 123 and overlaps ply 115. Ply 121 is thenplaced over portions of plies 115, 117, 119. Outward step 135 is formedwhere ply 121 lays over step 133 and the stacked portions of plies 115,117, with an inward step 137 occurring where ply 121 lays over edge 125.Another outward step 139 occurs where ply 121 meets edge 127, withlongitudinal portion 141 of ply 121 overlapping onto ply 119, edge 129being spaced from edge 127 of ply 119.

FIG. 3 shows another uncured laminated composite structure 143 with aprior-art splice joint formed in the manner described above. Asmentioned above, this method of construction prevents fibers of thevarious plies from moving relative to each other during consolidationand curing, and this often creates wrinkles in the finished structure.In addition, the outward and inward steps produced by the overlappingarrangement may cause stress concentrations due to discontinuitiesformed in the fibers of the plies.

To allow for fiber movement during consolidation and curing, therebyminimizing formation of wrinkles in the structure, the plies require acontraction/expansion joint in the uncured stack of layers. The splicejoint according to this disclosure consists of overlap, but instead ofrepeating the pattern every five plies, each layer is placed so thatspaces between edges of the plies of a layer form a V-shaped patternthrough the thickness of the laminate, allowing fibers of the plies tomove without being trapped by an overlapping ply.

While developed for use with AFP machines for highly convergent areas(e.g., double curvature with small radius), this approach can be usedwith hand-laid plies. The wrinkling phenomenon is mainly due to angulardeviation, and the only way to control the angular deviation of ahand-laid ply is by splicing it when the resulting angular deviation isout of the requirements. This is minimized in the AFP process, in whichan operator can be controlled and distribute the angular deviation of azone by finding a balance between isotropy and steering. Therefore, theusage of AFP allows the possibility to control each orientation (e.g., 0deg/45 deg/−45 deg/90 deg) to minimize fiber deviation on adouble-curvature shape. This control of the orientation and angulardeviation allows each ply to extend far enough to create the V-shapedpattern using AFP. The use of hand-laid plies would likely require anintermediate overlap to allow manufacturing because the material wouldexceed its allowable angular deformation (formability).

FIGS. 4 through 10 illustrate structures and methods according to thisdisclosure.

FIG. 4 is an exploded cross-section schematic view of a splice joint ina composite laminate structure 201 formed from layers of prepregcomposite plies. FIG. 5 is an enlarged detail view of the indicatedportion of the splice joint of FIG. 4. Structure 201 is formed by layingplies on a tool 203, plies being laid on a tool surface 205. Thoughshown as generally planar, tool surface 205 may be a small portion of alarger tool and may be a portion of a convex surface. The plies arearranged in a stack, with an offset overlap pattern forming the splicejoint. For this discussion, only the two innermost layers will bediscussed in detail, as the remainder of structure 201 is constructed ina similar manner. It should be noted that plies of structure 201 mayextend beyond the view shown in the figure.

Structure 201 comprises at least two layers A, B of plies of compositeprepreg, with base layer A being laid on tool surface 205, and layer Bbeing laid on layer A. As shown in FIG. 5, layers A, B comprise multipleparallel tapes 206 of unidirectional fibers laid adjacent one another,though it should be noted that plies of each layer A, B may be differentfrom those in other layers A, B and may differ within a layer A, B. Eachtape 206 has a pair of parallel longitudinal edges 207, 208 and an endedge 209 (only one shown) at each end of each tape 206. Layer Acomprises two plies 210, 211, and layer B comprises plies 212, 213. Inthe embodiment shown, plies 210, 211, 212, 213 are unidirectional tapehaving fibers extending parallel to the view plane (0 degrees), thoughother embodiments will have fibers generally perpendicular to the viewplane (90 degrees) or oblique to the view plane (e.g., +/−45 degrees).

Tapes 206 within plies 210, 212 extend longitudinally from a firstsection, and tapes 206 of plies 211, 213 extend longitudinally from asecond section, the first and second sections being joined by the splicejoint to form structure 201. In the embodiment shown, end edges 209 oftapes 206 of each ply 210, 211, 212, 213 form a gap edge for each ply210, 211, 212, 213. Ply 210 has gap edge 215, ply 211 has gap edge 217,ply 212 has gap edge 219, and ply 213 has gap edge 221. Plies 210, 211are laid on tool surface 205 in locations that place edge 215 of ply 210a selected contraction distance 223 from edge 217 of ply 211 to formcontraction gap 225. Plies 212, 213 are then laid on plies 210, 211 inlocations that place edge 219 of ply 212 over ply 211, such that edge219 is a selected splice distance 227 beyond edge 217 of ply 211. Inthis manner, ply 212 overlaps ply 211 by splice distance 227. Edge 221of ply 213 is a selected contraction distance 229 (which may be equal orunequal to distance 223) from edge 219 of ply 212 to form contractiongap 231. As shown in FIG. 4, additional layers may be added on top oflayers A, B, to form a desired thickness of structure 201. It ispreferable that two center layers C be located at the mid-thickness ofstructure 201 for creating a symmetric stack of layers, wherein one sideof the V-shaped overlap arrangement is formed on each side of centerlayers C.

Splice distance 227 may be an overlap distance determined by the plymanufacturer to achieve the desired minimum strength of structure 201after curing. However, contraction distances 223, 229 will be selectedbased on the calculated or expected amount that fibers of layers A, Bwill move toward tool surface 205 during consolidation and curing. Forexample, on a convex tool surface 205, loss of thickness in plies 210,211, 212, 213 will cause their fibers to move radially inward towardtool 203, and this will allow fibers of plies 210, 211 to move towardeach other in gap 225 and fibers of plies 212, 213 to move toward eachother in gap 231. In the ideal configuration, contraction distances 223,229 are selected to allow adjacent gap edges 215, 217 to butt togetherand for adjacent gap edges 219, 221 to butt together, but withoutcausing wrinkles to form in either layer A, B. The contraction distancebetween plies of a layer will typically increase as the radial distancefrom tool 203 increases for outer layers.

FIG. 6 is an exploded cross-section view of an embodiment of a structure301 having two splice joints according to this disclosure. Likestructure 201, structure 301 is formed from layers of prepreg compositeplies laid on a tool 303, plies being laid on a tool surface 305. Thoughshown as generally planar, tool surface 305 may be a small portion of alarger tool and may be a portion of a convex surface. The plies arearranged in a stack, with an offset overlap pattern forming the splicejoints. It should be noted that plies of structure 301 may extend beyondthe view shown in the figure. Plies 307, 309, 311 form layer A, andplies 313, 315, 317 for layer B. Longitudinal portions of ply 315overlap longitudinal portions of plies 307, 311 by a selected splicedistance, whereas plies within layers A, B are spaced from each other attheir adjacent gap edges by contraction gaps 319, 321, 323, 325. Asdescribed above for structure 201, the contraction distances defininggaps 319, 321, 323, 325 are selected to allow the fibers of each ply307, 309, 311, 313, 315, 317 to move toward the fibers of an adjacentply 307, 309, 311, 313, 315, 317 in a layer A, B as plies areconsolidated and cured. In this manner, contraction gaps 319, 321, 323,325 allow fibers to move close to each other or into contact duringconsolidation and curing without causing wrinkling of layers A, B.

FIGS. 7 through 9 illustrate what occurs during consolidation and curingof a structure having splice joints like structures 201, 301 andaccording to this disclosure.

FIG. 7 is a cross-section view of an uncured structure 401 having twosplice joints, as described above. Contraction gaps, such as gaps 402,403, are located in each layer of composite plies, and the plies areshown spaced from each other to indicate their uncured thickness. FIG. 8is a cross-section view of structure 401 of FIG. 7 after curing, and inwhich gaps 402, 403 are almost or completely closed as the thickness ofthe plies decreases during consolidation and curing. FIG. 9 is anoblique cross-section view of a section of cured structure 401. Asvisible in the figures, structure 401 after curing has layers of pliesthat lack the abrupt steps at overlap locations, such as those formedwhen using the prior-art methods for forming splice joints.

FIG. 10 is an exploded cross-section side view of another splice jointaccording to this disclosure and used in a composite laminate structure501 formed from layers of prepreg composite plies. Structure 501 isformed by laying plies on a tool 503, plies being laid on a tool surface505. Though shown as generally planar, tool surface 505 may be a smallportion of a larger tool and may be a portion of a convex surface. Theplies are arranged in a stack, with an offset overlap pattern formingthe splice joint. For this discussion, only the four innermost layerswill be discussed in detail, as the remainder of structure 501 isconstructed in a similar manner. It should be noted that plies ofstructure 501 may extend beyond the view shown in the figure.

In the embodiment shown, structure 501 comprises at least four layers A,B, C, D of plies of composite prepreg, with base layer A being laid ontool surface 505, layer B being laid on layer A, layer C being laid onlayer B, and layer D being laid on layer C. As shown, layers A, B, C, Dcomprise multiple tapes 506 of unidirectional fibers laid adjacent andparallel to one another within portions of each layer A, B, C, D, thoughit should be noted that plies of each layer A, B, C, D may be differentfrom those in other layers A, B, C, D and may differ within a layer A,B, C, D. Each tape 506 has a pair of parallel longitudinal edges 507,508 and an end edge 509 (only one shown) at each end of each tape 506.

Layer A comprises two plies 510, 511, layer B comprises plies 512, 513,layer C comprises plies 533, 535, and layer D comprises plies 537, 539.In the embodiment shown, plies 511, 537 are formed from tapes 506 havingfibers extending parallel to the view plane (0 degrees), plies 510, 512,513, 535 are formed from tapes 506 having fibers extending oblique tothe view plane (e.g., +/−45 degrees), and plies 533, 539 are formed fromtapes 506 having fibers extending generally perpendicularly to the viewplane (90 degrees). With this configuration, plies overlap onto plieshaving an identical fiber orientation, allowing for easier movement ofthe fibers of each overlapped ply during consolidation and curing. Tapes506 within plies 510, 512, 533, 537 extend from a first section, andtapes 506 of plies 511, 513, 535, 539 extend from a second section, thefirst and second sections being joined by the splice joint to formstructure 501.

In the embodiment shown, end edges 509 of tapes 506 of plies 510, 512,513, 535 are oblique to longitudinal edges 507, 508 and form gap edge515, 519, 521, 543, respectively. End edges 509 of tapes 506 of plies511, 537 are generally perpendicular to longitudinal edges 507, 508 andform gap edges 517, 545, respectively.

To form the splice joint, plies 510, 511 are laid on tool surface 505 inlocations that place edge 515 of ply 510 a selected contraction distance523 from edge 517 of ply 511 to form contraction gap 525. Plies 512, 513are then laid on plies 510, 511 in locations that place edge 521 of ply513 over ply 510, such that edge 521 is a selected splice distance 527beyond edge 515 of ply 510. In this manner, ply 513 overlaps ply 510 bysplice distance 527 with fibers oriented in the same direction in bothplies. Edge 519 of ply 512 is a selected contraction distance 529 (whichmay be equal or unequal to distance 523) from edge 521 of ply 513 toform contraction gap 531. As shown in the figure, plies 533, 535 oflayer C and plies 537, 539 of layer D are added on top of layers A, B inthe same overlapping manner to form contraction gaps 549, 551, with alloverlapping plies having the same fiber orientation as the overlappedplies. Additional layers may be added to form a desired thickness ofstructure 501.

As with the embodiments described above, it is preferable that twocenter layers be located at the mid-thickness of structure 501 forcreating a symmetric stack of layers, wherein one side of the V-shapedoverlap arrangement is formed on each side of center layers. Also,splice distances (overlap) may be determined by the ply manufacturer toachieve the desired minimum strength of structure 501 after curing, butcontraction distances will be selected based on the calculated orexpected amount that fibers of layers A, B, C, D will move toward toolsurface 505 during consolidation and curing.

At least one embodiment is disclosed, and variations, combinations,and/or modifications of the embodiment(s) and/or features of theembodiment(s) made by a person having ordinary skill in the art arewithin the scope of this disclosure. Alternative embodiments that resultfrom combining, integrating, and/or omitting features of theembodiment(s) are also within the scope of this disclosure. Wherenumerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example,whenever a numerical range with a lower limit, R_(l), and an upperlimit, R_(u), is disclosed, any number falling within the range isspecifically disclosed. In particular, the following numbers within therange are specifically disclosed: R=R₁+k*(R_(u)−R₁), wherein k is avariable ranging from 1 percent to 100 percent with a 1 percentincrement, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5percent, . . . 50 percent, 51 percent, 52 percent, . . . , 95 percent,96 percent, 95 percent, 98 percent, 99 percent, or 100 percent.Moreover, any numerical range defined by two R numbers as defined in theabove is also specifically disclosed.

Use of the term “optionally” with respect to any element of a claimmeans that the element is required, or alternatively, the element is notrequired, both alternatives being within the scope of the claim. Use ofbroader terms such as comprises, includes, and having should beunderstood to provide support for narrower terms such as consisting of,consisting essentially of, and comprised substantially of. Accordingly,the scope of protection is not limited by the description set out abovebut is defined by the claims that follow, that scope including allequivalents of the subject matter of the claims. Each and every claim isincorporated as further disclosure into the specification and the claimsare embodiment(s) of the present invention. Also, the phrases “at leastone of A, B, and C” and “A and/or B and/or C” should each be interpretedto include only A, only B, only C, or any combination of A, B, and C.

What is claimed is:
 1. A method for forming a composite structure offirst and second sections joined by a splice joint, each section beingformed from uncured layers of plies of composite material, each plybeing formed from fibers and a volume of uncured matrix material andhaving a gap edge, the method comprising: (a) placing a first ply of thefirst section on a convex surface of a tool; (b) placing a first ply ofthe second section on the surface of the tool, a gap edge of the firstply of the second section being spaced by a selected first contractiondistance from and generally parallel to a gap edge of the first ply ofthe first section, the first plies forming a first layer; (c) placing asecond ply of the first section on the first ply of the first section, agap edge of the second ply of the first section being spaced by aselected splice distance plus a selected second contraction distancefrom the gap edge of the first ply of the first section; (d) placing asecond ply of the second section on the first ply of the second section,a gap edge of the second ply of the second section being spaced by theselected second contraction distance from and generally parallel to thegap edge of the second ply of the first section, a portion of the secondply of the second section overlapping the first ply of the first sectionby the splice distance, the second plies forming a second layer, thefirst and second layers forming a splice joint; (e) consolidating thelayers and curing the matrix material, thereby causing contraction ofthe layers toward the tool, the first and second contraction distancesbeing selected so that adjacent gap edges of the plies of each layer arein close proximity or in contact after moving toward each other duringthe contraction, the second contraction distance being larger than thefirst contraction distance.
 2. The method of claim 1, furthercomprising: repeating steps (c) and (d) to place additional layers priorto step (e), a contraction distance for each additional layer beinglarger than a contraction distance in an adjacent previous layer.
 3. Themethod of claim 1, further comprising: repeating steps (c) and (d) toplace additional layers prior to step (e), a contraction distance foreach additional layer being larger than a contraction distance in anadjacent previous layer, the additional layers being arranged to form astack of layers symmetric about a thickness of the stack.
 4. The methodof claim 1, further comprising: forming a second splice joint in thelayers to join a third section to the first and second sections.
 5. Themethod of claim 1, wherein the tool has a closed shape.
 6. The method ofclaim 1, wherein the tool has an open shape.
 7. The method of claim 1,wherein the plies are formed from unidirectional fibers.
 8. The methodof claim 1, wherein the plies are formed from unidirectional fibers, andsteps (c) and (d) comprise orienting the fibers of the second layer atan angle to the fibers of the first layer.
 9. The method of claim 1,wherein the fibers of the first ply of the first section and of thesecond ply of the second section are oriented in the same direction. 10.The method of claim 1, wherein the gap edges of the second plies aregenerally parallel to the gap edges of the first plies.
 11. The methodof claim 1, further comprising: repeating steps (c) and (d) to placeadditional layers prior to step (e), the additional layers beingarranged so that gaps formed between gap edges of each layer form aV-shaped pattern through the thickness of the structure.
 12. A methodfor forming a closed-shape composite structure of first and secondsections joined by a splice joint, each section being formed fromuncured layers of plies of composite material, each ply being formedfrom fibers and a volume of uncured matrix material and having a gapedge, the method comprising: (a) forming a first layer by placing afirst ply of each of the first and second sections on a convex surfaceof a mandrel, gap edges of the first plies being spaced by a selectedfirst contraction distance from each other, thereby forming a gapbetween the gap edges of the first plies; (b) placing a second ply ofthe first section on the first ply of the first section, a gap edge ofthe second ply of the first section being spaced by a selected splicedistance plus a selected second contraction distance from the gap edgeof the first ply of the first section; (c) placing a second ply of thesecond section on the first ply of the second section, a gap edge of thesecond ply of the second section being spaced by the selected secondcontraction distance from and generally parallel to the gap edge of thesecond ply of the first section, thereby forming a gap between the gapedges of the second plies, a portion of the second ply of the secondsection overlapping the first ply of the first section by the splicedistance, the second plies forming a second layer, the first and secondlayers forming a splice joint; (d) consolidating the layers and curingthe matrix material, thereby causing contraction of the layers towardthe mandrel, the first and second contraction distances being selectedso that adjacent gap edges of the plies of each layer are in closeproximity or in contact after moving toward each other during thecontraction, the second contraction distance being larger than the firstcontraction distance.
 13. The method of claim 12, further comprising:repeating steps (b) and (c) to place additional layers prior to step(d), a contraction distance for each additional layer being larger thana contraction distance in an adjacent previous layer.
 14. The method ofclaim 12, further comprising: repeating steps (b) and (c) to placeadditional layers prior to step (d), a contraction distance for eachadditional layer being larger than a contraction distance in an adjacentprevious layer, the additional layers being arranged to form a stack oflayers symmetric about a thickness of the stack.
 15. The method of claim12, further comprising: repeating steps (b) and (c) to place additionallayers prior to step (d), a contraction distance for each additionallayer being larger than a contraction distance in an adjacent previouslayer, the additional layers being arranged so that the gaps form aV-shaped pattern through the thickness of the structure.
 16. The methodof claim 12, further comprising: forming a second splice joint in thelayers to join a third section to the first and second sections.
 17. Themethod of claim 12, wherein the plies are formed from unidirectionalfibers.
 18. The method of claim 12, wherein the plies are formed fromunidirectional fibers, and steps (b) and (c) comprise orienting thefibers of the second layer at an angle to the fibers of the first layer.19. The method of claim 12, wherein the fibers of the first ply of thefirst section and of the second ply of the second section are orientedin the same direction.
 20. The method of claim 12, wherein the gap edgesof the second plies are generally parallel to the gap edges of the firstplies.